While this article
specifically addresses a spider and holder for an 8" Newtonian it can be
used as a basis for constructing any curved vane spider or secondary holder.

Above are all of the
parts you will make or buy except the mounting bolts, washers and nuts used to
hold the spider to the tube. The parts shown include the spider, the holder with
diagonal mounted, retaining and adjusting knob, shaft washers, spring washers,
and central obstruction stop. Of course, you can always buy a holder to fit the
hub. There are some nice ones out there. Check to see what various makers use
for a central mounting shaft. Some use a 3/8"-16 thread and some use
1/4-20. Europeans will have their own metric sizes to consider. The threaded rod
is nice because you can adjust to the correct distance by simply turning it to
the next thread position and locking it down with a nut or threaded knob (McMaster-Carr
or Reid Supply in the US).